1. Field of the Invention
This invention relates to thermally compensating positioning devices for use in maintaining an object in a precisely fixed position throughout ambient temperature fluctuations. In particular, it concerns positioning units that enable optical mirrors or other objects requiring precise positioning regardless of ambient temperature fluctuations to be operatively mounted on support structures that undergo dimensional change with temperature changes.
2. Description of the Prior Art
The need to provide, in some fashion, compensation for differences in thermal expansion between parts in structures is universal. In many instances, minimal precision of such compensation is required, e.g., expansion joints between sections roadways. In other cases, however, greater compensation precision is required.
One type of structure that requires high precision in thermal compensation for thermal expansion between parts is optical devices such as optical telescopes and other optical instruments. While such need exists for terrestrial devices, the requirements and demands on thermal compensation become exaggerated in connection with devices designed for extra-terrestrial use because of the extreme temperature variations that will be encountered by such devices, e.g., between 0.degree. and 600.degree. K. and, particularly, between -130.degree. and 200.degree. C.
One approach towards mitigating the problem of temperature expansion differentials of parts in structures, including optical devices, has been to use materials having substantially zero coefficient of thermal expansion for construction of parts, e.g., "Invar" metal. For example, U.S. Pat. No. 4,157,802 discloses the use of such material in conjunction with a rigid, thermally sensitive base to provide support for optical elements that must be held immobile through a range of ambient temperatures.
The use of zero or nearly zero coefficient materials to avoid parts movements due to temperature changes in optical or other devices is disclosed in a variety of other prior U.S. Pats. Nos. including:
2,533,478, 3,484,718,
2,537,900, 4,282,688.
The present invention provides further improvements in the art of thermal parts differential compensation making possible the positioning of objects, e.g., optical mirrors, throughout wide temperature ranges with a precision of the order of an Angstrom unit.